Friday, November 28, 2014

When I was a grad student twenty-some years ago, my profs knew me as a
guy who liked to come up with his own way of analyzing things. My
thesis advisor was in Electrical Power, and everything there is done by
"modelling". You have a motor or a transformer, and there is a "model"
which represents its internal parameters like "core losses" or
"magnetizing inductance". You do some external measurements from which
you calculate those parameters, and then you analyze the machine as a
simple circuit using the parameters you just calculated.

I
never did this. I always worked from physical logic and analyzed things
from the ground up. Once my advisor asked me, "Marty, why don't you
like models?" (He was Rob Menzies, actually a very capable engineer and a
pretty good prof.) I told him I didn't like them because they
encouraged you to work by numbers without actually understanding what
you were doing. I don't know if he got my point, but the other day I had
a flashback to that moment.

I was working with some
Engineering students the other day and one of them asked me a question
from his Power Systems course. It was about transformers. You do some
measurements on the transformer and calculate its equivalent circuit
parameters. I asked him to show me the question, and he did. It started
off something like this:

"You
have a single-phase transformer rated 20 kVA, 2200V primary and 220
secondary. You do an open circuit test and measure 220V, 2.5 A and 100
Watts. Then you do the short circuit test and measure 150V, 4.5A and 250
Watts. Determine the equivalent circuit parameters."

I
asked him to show me how those measurements were done. So he started to
draw out the circuit model, which looks something like this:

Okay,
I said, where do you measure the 220 volts? He started to point to one
of the components, I don't remember which one, it might have been Xm,
and I said: "No, you can't measure the internal parameters, those are only theoretical constructs. You can only measure the actual transformer".

He didn't exactly get it. So I drew this picture:

"THIS
is what a transformer looks like", I told him. "There are only four
wires. You have a voltmeter, an ammeter, and a wattmeter. Where do you
hook them up?"

He was stumped. He had to admit that he had no idea.
They never talked about that in class. The prof told them that there was
something called an "open circuit test" and something called a "short
circuit test", that you get these measurements, and then you put them
into these formulas, and the result is the equivalent circuit parameters
(the ones you see all over the transformer model in the first diagram).
No one ever talked about what it actually means.

And
that's why I don't like models. Because they fool you into thinking
that you know what you're doing, when you really don't. Actually, this
particular student was pretty smart. He recognized right away that he'd
been strung along, but he'd gone along with it because he had no choice.
You follow directions or you fail. There's no time to second-guess the
system and question what you're learning. And that makes him an
exception.

The problem with education system is that by
the time they've gotten this far, most students are no longer capable
of recognizing what's wrong with the whole scenario. If I'd have
confronted the typical engineering student with the fact that he was
doing the calculation blindly even though he didn't even know where the
voltmeter was supposed to be hooked up, he would have simply replied
that it didn't matter, that you didn't need to know that stuff
because the right way to do it was just to follow the steps that the
professor had laid out. And he would get the right answer on the test.

But
that's not the biggest problem. The real tragedy of the education
system is that it is doing exactly what society demands of it: churning
out obedient workers for the government/industrial bureaucracy who will
do what they are told without questioning or even trying to understand
the reason behind it.